For example, a solar heat collection system used for solar thermal power plants described in Patent Document 1 is known in the art. Patent Document 1 describes a configuration of “a solar heat boiler including a low temperature heating device that heats water supplied from a water supply pump by solar heat; a steam separation device that separates two-phase water-steam fluid generated in the low temperature heating device into water and steam; a high temperature heating device that heats the steam separated in the steam separation device by solar heat; and a circulating pump that supplies the water separated in the steam separation device to the low temperature heating device” (see Abstract).
In the configuration of Patent Document 1, a low-temperature heating device of linear light focusing type such as trough type or Fresnel type is used, and a heat collecting device of tower type is used as a high temperature heating device. According to Patent Document 1, the light focusing and heat collecting device can be reduced in size. Thus, the construction cost can be reduced by reducing the height of the tower. Additionally, the light focusing accuracy required for heliostats is in proportion to the height (distance) of the tower, and thus costs required to maintain the light focusing accuracy high, such as costs of adjusting angles during construction and operation, can be reduced.